Often complaints are with the particular problems which purportedly will require novel solutions or be very difficult, rather than with this methodology in the abstract. These objections often go with "we'll cross that bridge when we come to it," but it's not a fully general version of "we'll cross that bridge when we come to it."
For example, often these problems cannot be or have not been modeled in any explicit way. For example, no one has precisely or clearly articulated a possible capability state in which our lack of understanding of self-referential reasoning leads to catastrophic trouble. If we had such a capability state in mind, it would serve both as an argument that the problem may be critical, and moreover as a way of determining what exactly the problem is.